Vacuum pumps such as turbomolecular vacuum pumps are often employed for evacuating process chambers used in manufacturing. Although turbomolecular pumps are efficient in removing many gases from process chambers, they are not efficient for pumping water vapor. As a result, cold traps are commonly mounted in-line between the turbomolecular pump and the process chamber for improving the water pumping capabilities. Such cold traps remove water vapor from the process chamber by condensing the water vapor on a cryopumping array positioned in the fluid flow path.
Most cold traps include a fluid conduit having flanges at opposite ends for mounting in-line between the process chamber and the turbomolecular pump. The cryopumping array is positioned within the fluid conduit and is cooled by a cryogenic refrigerator. Some cold traps are designed to provide minimal flow resistance for non-condensing gases passing therethrough such as nitrogen and argon by employing a thin walled tubular cryopumping array. The most common tubular array is about 8 inches in diameter by 6 inches long. A tubular array of this size results in a cold trap having a fluid conduit about 9 inches long. The water vapor condenses along the surfaces of the tubular array while allowing the non-condensing gases to pass substantially unrestricted through the open center of the array. Typically, a gate valve is mounted between the cold trap and work chamber to permit isolation of the two.